This invention relates to a system for integrally controlling an automatic transmission and an engine, and more particularly to improvements in a system for integrally controlling an automatic transmission and an engine, wherein the engine ignition timing is temporarily lagged during shifting to decrease engine torque.
Automatic transmissions comprising gear transmission mechanisms, a plurality of frictionally engaging devices, and hydraulic pressure control devices operated to selectively switch the engagements of the frictionally engaging devices, so that any one of a plurality of gear stages can be achieved in accordance with a preset shift map, are well known in the transmission art.
Furthermore, in an automatic transmission for a vehicle of the type described, various systems have been implemented for integrally controlling an automatic transmission and an engine, wherein engine torque is changed during shifting to obtain satisfactory shift characteristics and durability of the frictionally engaging devices (For example, Japanese Patent Laid-Open No. 69738/1980). More specifically, in such system the amount of torque transmitted from the engine is changed during shifting and the amount of absorbed energy in various members in the automatic transmission or in the frictionally engaging devices for controlling these members is controlled so as to complete a shifting within a short period of time under a low shift shock. As a consequence, drive comfort is enhanced and durability of the frictionally engaging devices is improved.
However, when ignition timing is delayed as a method of changing (decreasing) engine torque during shifting, problems are encountered. One such problem is the increase in so-called after-burn. After-burn is caused by the opening of an exhaust valve before complete burning of the gaseous mixture in the engine cylinders due to the delay of ignition timing. As a result of after-burn, high temperature burning gas is exhausted into the exhaust pipe, causing the temperature of the exhaust system (exhaust gas temperature, catalyst temperature, exhaust pipe temperature and the like) to rise.
However, when running in mountainous areas, where the shift frequency is high, or where a user intentionally performs on-off operations of an accelerator, the temperature of the exhaust system rises to a tolerance value or more, and in an extreme case, durability of the exhaust manifold is reduced. Further, in a turbo-charged engine system the temperature of the exhaust system can have an adverse impact on the durability of the turbine blades on the exhaust side.
One countermeasure for attempting to obviate the above-described disadvantages is to design a routine relating to the engine torque control which sets the map of the engine torque change value, assuming shiftings are performed at the expected highest frequency. However, with this method, the reduction value of the engine torque during shifting is naturally decreased, with the result that improvement of shift characteristics, including the durability of the frictionally engaging devices, cannot be satisfactorily achieved.
Another countermeasure to obviate such disadvantages is to increase the fuel injection flow rate while performing lag angle control (ignition timing delay control), to thereby lower exhaust gas temperature. However, according to this method, if the fuel increase is performed simultaneous with or after the lag angle control is carried out, little or no lowering of the exhaust gas temperature is advantageously obtained.